Internet speed drops significantly on access point connected to CGNM-3552

[The_One]

I have a Hitron CGNM-3552 (192.168.0.1) and a TP-Link AC1900 Archer C80 (192.168.0.2 in access point mode) connected together via a LAN cable. The LAN speed of this connection on TP-Link shows 1gbps. I believe the LAN speed on the CGNM is also 1gbps because the LAN port light on the back is Yellow. I removed all other LAN connections on both devices.

I performed internet speed tests (using the Rogers tool) connecting to either router and the are similar (around 200mbps download/10mbps upload).

The problem occurs when I plug anything into one of the other CGNM LAN ports. When anything is plugged in, the download speed on the TP-Link access point drops to 60 mbps. The upload speed is unchanged.  When I unplug the additional LAN connection from the CGNM, the internet speed goes back up TP-Link. It doesn't matter what I plug in (TV, Chromecast, Philips HUB, etc.), I can reproduce this behavior every time. This occurs even if the device plugged in is off. Note, the plugged in device shows green on the LAN port connection on the back.

On the CGNM, the download/upload speeds don't change. So it seems like the CGNM has a problem using a 1gb and 100mb connections. Any suggestions?

***Added Labels***

[RogersYasmine]

Hello, @The_One!

Thanks so much for joining us in the forums and for sharing your concerns with the community! 🙂

Unfortunately, we wouldn't be able to support or advise on any third party configurations, however, perhaps one of our knowledgeable Resident Experts may have some advice they can share. I'll tag some of them into this post for you: @Datalink @-G- @Gdkitty

Cheers!

RogersLaura

[-G-]

@The_One  I don't know the Hitron modems well but I don't see why having mixed-speed LAN devices connected should have any effect on throughput.

Do you happen to have a small Gigabit Ethernet LAN switch on hand?  I'm curious to see whether you have the same issues with all devices connected to the external switch, and nothing but the switch connected to your modem's LAN ports.

[The_One]

Thanks for replying.

No I don't have Gigabit LAN switch.

With only the TP-Link connected to the CGNM, I get equivalent speeds. When I plug devices into the LAN ports on the TP-Link, the speeds are the same. This only occurs when one additional device is plugged into the CGNM.

[Datalink]

@The_One this is certainly an odd case.  

1.  Is this a recent development?  If so, what firmware version are you running on the 3552 modem?

2.  If this isn't a recent development, please confirm for me that its always been this way.  

The connected port LEDs at the back of the modem will flash amber for a 1 Gb/s connection with the connected device.  They will flash green for a 100/10 Mb/s connection rate with the connected device.  

Reading thru your posts, I'm thinking that its possible that some of the devices that you have are only equipped with 100 Mb/s ports.  Do you have any ethernet devices with gig ethernet ports that you can plug into the router and actually confirm in the router's user interface that the device is connected at a 1 Gb/s rate.  That connection rate is independent of the actual internet plan that you're on.  

Ok, where I'm going with this is to be able to connect two devices that are equipped with serviceable 1 Gb/s ethernet ports into any of the modem's ports.  In theory, with those devices connected, both ports on the modem should be running at 1 Gb/s and the LEDs should be flashing amber.  If you run a speed test on either device, what do you get for data rates? 

Now, if you connect a second device with an operating gig port into the modem and the modem shows a 100/10 Mb/s as shown with a green flashing LED instead of flashing amber indicating a gig connection rate, or you end up with sub 100 Mb/s for a data rate thru the gig port, then there is a problem.  

If you connect a second device with known 100/10 Mb/s port and the data rate thru the other gig port slows down to sub 100 Mb/s, then there is a problem.  

So, that leads to one conclusion, there is a firmware or port controller issue with the modem.  @RogersIan posted a new firmware version for the CGN3AC modem about three weeks ago.  That should probably include the CGNM-3552 modem as well, although its not mentioned in the post.  The version in the post is 4.5.8.47.

https://communityforums.rogers.com/t5/Internet/FEEDBACK-Rogers-Rocket-Wi-Fi-Modem-Firmware-Trial/m-p...

So, that's why I'm wondering if this was a recent development as it can take several weeks to roll out a firmware version across the network.  

First step that I'd take is to reboot /restart the modem just to see what difference that makes, if any .... ADMIN .... DEVICE RESET .... Reboot.  Then I'd run a factory reset, again to see what difference it makes, if any .... ADMIN .... DEVICE RESET .... Factory Reset.  

Then I'd consider the firmware version.  If you're running version 4.5.8.47 now I'd consider the possibility of a firmware problem that wasn't detected in the release testing.  

After that, I'd consider the possibility of a port controller failure.

Out of curiosity, is there a reason that the modem is running in Gateway modem with a router behind it.  In that configuration you're running a double Network Address Translation scheme, where both the modem and router are translating the inbound data from the WAN side of the modem or router to their respective LAN ports and IP addresses.  Yes, that does work, but, its inefficient, especially for gaming.  

Just a thought, when you plug a second device into the modem, it should be connected when its off, and then started.  If you connect a device to the modem, that was just disconnected from the router, and its still running, there is a good chance that the device will not accept the IP address assigned to it by the modem.  It will still be running its previous IP address, believing that is still connected to the router.  So, you would end up in a situation where the modem has its own operating IP address range, and now, it has a device connected that has an IP address outside of that range.  This would be a totally strange situation with two potential IP addresses for the same device and the possibility of strange results.  So, if you connect a device to the modem, it should be connected when its off, or, if its still running after disconnecting from the router, restart the device.  If you're still seeing issues, restart the modem, ADMIN .... DEVICE RESET .... Reboot.

[The_One]

Thanks again for responding. The reason I'm running the CGNM in Gateway mode is because I need 6 LAN ports (TV, chromecast ultra, phillips hue, etc.)  Also the location of the CGNM is resulting in a weak connection to the wireless doorbell.

1. The firmware version is 4.5.8.45. The Hardware version is 1A. 

2. I can't say this is a recent development since the first time I've connecting another modem as an access point was a week before writing this post.

I did another test with an old DLink-825 as an access point (LAN to LAN flashing amber) and it yielded the same results. Download speed drops to about 1/4 speed when another device is attached to the CGNM LAN port (flashing green). The Upload speed is always consistent everytime.

When I connect both the DLink and TP-Link, both LAN ports flash amber and once again, the speed drops on the TP-LINK, however it seems to drop to about 1/4 to 1/2 the speed, not consistent but a little quicker than above.

I tried using different combinations of LAN ports and one thing I see is when using the port second from the bottom, only this port would flash once amber when I plug the cable in, and then stay flashing green. The port speed on this port is the same as above in this case with the TP-Link plugged in.

Thanks for the upgrade link, however it doesn't point to a location when I can download a file.

The TP-Link has a built in Access Point mode allowing the cable to be connected CGNM LAN to TP-Link WAN. Not sure what this mode fully does, but I think it disables a lot of the modem features and makes just a wireless access point (some options/configuration disappears on the TP-Link menu when this is enabled.) 

I will try connecting the other devices while the modem is off. I've done several restarts over the past weeks and it didn't seem to help.

[The_One · Accepted solution]

Just wanted to thank you for your feedback. I did more testing and I found that the access point wasn't the problem. I still think the problem is with the CGNM. I started a new post to point out how I was able to prove this.

https://communityforums.rogers.com/t5/Internet/Slow-internet-speeds-on-LAN-connect-devices-on-CGNM-3...